FIELD OF THE INVENTION
This invention relates to a method of refining pulp stock in which the pulp material to be ground is introduced into a grinding space located between a first rotatable grinding device carried by a shaft and being axially displaceable by a servo motor, and a second non-rotatable grinding device. The servo motor is actuated by pressurized fluid for adjusting and controlling the grinding space, producing a grinding pressure between the first and the second grinding devices, and for preventing axial displacement of the first rotatable grinding device relative to the second non-rotatable grinding device in response to fluctuating axial grinding forces. The second non-rotatable grinding device includes a plurality of concentrically arranged annular grinding members, at least one of which is axially adjustable by a setting device.
The invention also relates to a grinding apparatus which includes grinding discs in opposed relationship, and forming a grinding space therebetween. A rotatable grinding member is carried by an axially displaceable shaft, and the axial position of the shaft determines the size of the grinding space. The space is controlled and maintained by a servo motor, as exemplified in U.S. Pat. No. 2,964,250. The stationary grinding disc comprises two or more concentrically arranged, annular members for grinding disc elements, which are axially adjustable relative to each other to form the most efficient contour of the grinding space.
The grinding product, such as lignocellulosic material from wood chips or the like, is fed into an opening at the grinding space and forced through the grinding discs primarily in an outward radial or spiral direction by centrifugal forces in combination with the feeding effect of the grinding disc patterns used. During this forced passage by the grinding discs, the treated material generates a high grinding pressure which is transferred to the grinding members as axial forces that are absorbed and counteracted by a rotary side hydraulic main servo motor acting on the rotatable shaft with its grinding member and, on the stator side, by set screws of the adjustable annular grinding members and directly by the stator base of the non-adjustable part of the stationary grinding member.